Although the sheet feeding art is quite old, modern electrostatic copiers and electronic scanners have required its perfection. The most critical sheet feeding task in a scanner is the document handler. In order to maintain the page sequential order of a stack of original document sheets, the sheets are commonly fed off the bottom of the stack. Because of the weight of the stack, bottom separation is difficult and limits the height of the stack and a top sheet feeder would be desirable.
Document originals often vary in size, weight, age and condition. However, nearly all document handlers presently on the market come with instructions not to feed originals of unusual weight or of poor condition. A feeder which can handle a wide variety of types of originals would also be desirable.
Document feeders for sheet materials typically consist of three basic elements, commonly an urging means such as a roller or belt, a feed means such as a roller or belt, and a retard means or separation device. The urging means imparts a force to the sheet being fed and directs it into the feed means. The feed means transports the sheet to the imaging transport path. The retard means is intended to hold back the other sheets in the stack so that only one sheet is fed into the imaging means at one time.
In a document scanner it is desirable to transport single sheets as described above one-by-one from a stack into the imaging transport. It is also desirable to be able to feed odd documents such as stapled documents, very thin documents, or documents in a protective covering, that would not normally feed well through conventional document feeders that use a retard or separation means. A device that would allow easy conversion between manual feed, where the separation force is removed, and auto feed, would be highly desirable.
In certain situations, it is desirable to disengage or remove the separation means from the paper path for cleaning or replacement. Currently available scanners provide for moving the separation means away from the document by depressing a lever. However, these models use separation rollers that are counter driven and require a drive means associated with the separation means. A device that avoids such rollers would be smaller and more easily serviced.